With the high-integration and high-miniaturization of semiconductor integrated circuits, the miniaturization of Metal Insulator Semiconductor Field Effect Transistors (MISFET) on the semiconductor integrated circuits is advancing. With the miniaturization, the thickness of a gate insulator is demanded to be extremely thin, being about a couple nanometers.
Generally, silicon oxide (SiO2) film, which is formed by thermal oxidation of a silicon substrate, is applied as a gate insulator. However, thinning a silicon oxide film to a couple nanometers, has problems such as an increase of the gate leakage current (tunnel current), and penetration of impurities from the gate electrode of the MISFET.
To control the increase and so forth of the tunnel current, a stacking gate insulator which has a structure of stacking a higher permittivity film (high-permittivity film) onto a thin-silicon oxide film (or a silicon nitride film, or a silicon oxide-nitride film), is being developed. By applying the stacking gate insulator, physical thickness is secured to a certain extent, and Equivalent Oxide Thickness (EOT) is kept low. Here, the EOT is a converted value of the thickness of the film of the relative permittivity ε and effective film thickness t, to the thickness of the relative permittivity of the silicon oxide film (εsio2/ε), and is defined as, EOT=(εsio2/ε)·t.
A forming method of a stacking gate insulator applying a silicon nitride film (SiN film) as a high-permittivity film has been disclosed in the Unexamined Japanese Patent Application KOKAI Publication No. 2000-294550. The insulated gate formed by the method disclosed in the aforementioned publication, comprises a direct silicon oxide-nitride film (or an oxide film or a nitride film) formed in a thickness of one nanometer or less, applying a plasma processing device including a Radial Line Slot Antenna (RLSA), and a SiN film, formed in about 2 nanometers on this oxide-nitride film by CVD.
When an RLSA-type plasma processing device is applied, a more high-quality film with less dangling bond is formed, compared to being formed by a CVD. Also, because the film forming processing, applying the RLSA plasma processing, is conducted in a relatively low temperature (250°˜450°), the damage of the film surface is decreased compared to other plasma processing. In this way, films formed by applying the RSLA-type plasma processing is high in quality, therefore annealing in a high temperature, at about 1000°, is not necessary, and diffusion of dopant can be prevented.
Here, the aforementioned stacking gate insulator applies the SiN film as the high-permittivity film. The relative permittivity of the SiN film is about 8, therefore the EOT of the SiN film is only about 0.5 (=4/8) times the effective film thickness. Due to this, when the SiN film is applied, there is a limit to securing a sufficiently thick physical film thickness, and gaining a sufficiently thin EOT by answering to the demand of miniaturization.
By this, when inorganic insulation films with higher relative permittivity, for example, aluminum oxide (relative permittivity:11), zirconium oxide (24), and hafnium oxide (25) are applied, an EOT about 0.17 (=4/24) times the effective film thickness can be gained.
As aforementioned, by applying an inorganic high-permittivity film, a requested gate insulator having the requested permittivity can be gained. However, if an organic high-permittivity film is directly formed onto the silicon oxide film, the silicon oxide film and the organic film will cause a reaction. By this, the EOT of the whole stacking gate insulator will increase.
Generally, the aforementioned inorganic high-permittivity films are formed, for example, by applying an organic metal such as ethoxide metal as the precursor, by CVD. By this, the formed high-permittivity film includes a few percent of carbon. When the carbon content is high, reliability declines, such as the occurrence of the leakage current increasing.
In this way, hitherto, it was difficult to generate a highly reliable gate insulator having a sufficient physical thickness and a sufficiently thin EOT.